Make use of interfaces

Use an interface instead of serf.Serf as arg to NewServerManager.  Bonus points for improved testability.

Pointed out by: @slackpad

consul/server_manager/server_manager.go

@@ -9,7 +9,6 @@ import (
 
 	"github.com/hashicorp/consul/consul/server_details"
 	"github.com/hashicorp/consul/lib"
-	"github.com/hashicorp/serf/serf"
 )
 
 type consulServerEventTypes int
@@ -61,6 +60,10 @@ const (
 	defaultClusterSize = 1024
 )
 
+type ConsulClusterInfo interface {
+	NumNodes() int
+}
+
 // serverCfg is the thread-safe configuration structure that is used to
 // maintain the list of consul servers in Client.
 //
@@ -94,7 +97,7 @@ type ServerManager struct {
 	// serf is used to estimate the approximate number of nodes in a
 	// cluster and limit the rate at which it rebalances server
 	// connections
-	serf *serf.Serf
+	clusterInfo ConsulClusterInfo
 }
 
 // AddServer takes out an internal write lock and adds a new server.  If the
@@ -179,11 +182,11 @@ func (sm *ServerManager) getServerConfig() serverConfig {
 
 // NewServerManager is the only way to safely create a new ServerManager
 // struct.
-func NewServerManager(logger *log.Logger, shutdownCh chan struct{}, serf *serf.Serf) (sm *ServerManager) {
+func NewServerManager(logger *log.Logger, shutdownCh chan struct{}, cci ConsulClusterInfo) (sm *ServerManager) {
 	// NOTE(sean@): Can't pass *consul.Client due to an import cycle
 	sm = new(ServerManager)
 	sm.logger = logger
-	sm.serf = serf
+	sm.clusterInfo = cci
 	sm.consulServersCh = make(chan consulServerEventTypes, maxConsulServerManagerEvents)
 	sm.shutdownCh = shutdownCh
 
@@ -289,12 +292,7 @@ func (sm *ServerManager) refreshServerRebalanceTimer(timer *time.Timer) {
 	clusterWideRebalanceConnsPerSec := float64(numConsulServers * newRebalanceConnsPerSecPerServer)
 	connReuseLowWatermarkDuration := clientRPCMinReuseDuration + lib.RandomStagger(clientRPCMinReuseDuration/clientRPCJitterFraction)
 
-	// Assume a moderate sized cluster unless we have an actual serf
-	// instance we can query.
-	numLANMembers := defaultClusterSize
-	if sm.serf != nil {
-		numLANMembers = sm.serf.NumNodes()
-	}
+	numLANMembers := sm.clusterInfo.NumNodes()
 	connRebalanceTimeout := lib.RateScaledInterval(clusterWideRebalanceConnsPerSec, connReuseLowWatermarkDuration, numLANMembers)
 	sm.logger.Printf("[DEBUG] consul: connection will be rebalanced in %v", connRebalanceTimeout)
 

consul/server_manager/server_manager_internal_test.go

@@ -22,10 +22,17 @@ func GetBufferedLogger() *log.Logger {
 	return localLogger
 }
 
+type fauxSerf struct {
+}
+
+func (s *fauxSerf) NumNodes() int {
+	return 16384
+}
+
 func testServerManager() (sm *ServerManager) {
 	logger := GetBufferedLogger()
 	shutdownCh := make(chan struct{})
-	sm = NewServerManager(logger, shutdownCh, nil)
+	sm = NewServerManager(logger, shutdownCh, &fauxSerf{})
 	return sm
 }